Dual-pressure hydraulic system



I INVENTOR. QDOLPH J. DE MHTTEO HTTOQNE 7's Dec. 3, 1957 A. J. p5: MATTEFO DUAL-PRESSURE HYDRAULIC SYSTEM Filed 001;. 29, 1956 DUAL-PRESSURE HYDRAULIC SYSTEM Adolph J. De Matteo, Berkeley Heights, N. J., assignor to Farrel-Birmingham Company, Inc., Ansonia, Conn, a corporation of tlonnecticut Application October 29, 1956, Serial No. 618,834

6 Claims. (Cl. 137-120) The present invention relates generally to hydraulic pressure systems and more particularly to a system entailing both low and high pressure pumps adapted cooperatively to feed low and high pressure accumulators so as to maintain the desired fluid levels therein.

in the working of hydraulically-operated extrusion presses, the high pressure water is supplied from motordriven vertical or horizontal pumps. The large size of many modern presses and the need for high speed operation render almost imperative the use of some form of high pressure power-storing device or accumulator in conjunction with low pressure storage vessels supplying power for the idle motions of the press. Normally the requirements for low pressure water are much higher than for high pressure, as a result of which several low pressure pumps are included in the conventional installation to deliver a large volume of water. These low pressure pumps are very costly and add substantially to the total cost of the installation.

In view of the foregoing, it is the principal object of this invention to provide a dual-pressure hydraulic system including both low and high pressure pumps, which system etfects a substantial economy in the number of low pressure pumps entailed. The system in accordance with the invention has a low pressure water capacity equal to or exceeding that of a conventional system having a greater number of low pressure pumps.

More specifically, it is an object of the invention to provide a dual-pressure system, as above described, wherein the high pressure pumps act intermittently to supply water to the low pressure accumulator, the operation being eilectcd automatically when water in the high pressure accumulator is at a desired maximum level and a demand is registered for low pressure water.

A significant feature of the invention resides in the fact that the low pressure pumps continuously feed the low pressure accumulator, whereas the high pressure pumps act to feed the low pressure accumulator as well as the high pressure accumulator. Inasmuch as there is a lesser demand for high pressure, the intermittent action of the high pressure pumps to supply the low pressure accumulator reduces low pressure pump requirements and makes it possible to operate with fewer low pressure pumps.

Also an object of the invention is to provide a hydraulic system of eflicient and reliable design which may be manufactured at relatively low cost.

For a better understanding of the invention, as well as other objects and further features thereof, reference is had to the following detailed description to be read in conjunction with the accompanying drawing, whose single figure shows schematically a dual-pressure system in accordance with the invention.

Referring now to the drawing, there is shown a hydraulic system comprising a bank 10 of two high pressure pumps and a separate bank 11 of three low pressure pumps. The pumps in each bank operate collectively to meet the low pressure and high-pressure requirements of ateht O the system. be of the 5,000 p. s. i. type and the low pressure pumps of the 2,500 p. s. i. type. The number and capacity of the pumps involved will of course depend on the requirements of the system.

Also provided is a high pressure accumulator 12 and a low pressure accumulator 13 of standard design. The output of accumulator 12 is fed via a conduit 14 through a suitable control valve 15 to a hydraulic cylinder 16, the output of accumulator 13 being fed to the same cylinder via conduit 17 and a control valve 18. Thus by operation of valves 15 and 18 high or low pressure fluid may be supplied to the cylinder.

The cylinder acts through the usual piston means to drive a ram, to close a gripper or any other device requiring pressure, the low pressure serving a carry out the idle movements and the high pressure the working movements of the device. It is to be understood that many metal-working presses, stretch-forming machines and other known pressure-operated mechanisms conventionally make use of dual-pressure hydraulic systems. The present invention, however, provides a novel arrangement for effecting an economy in the pump requirements for such systems.

In the hydraulic system of standard design the low pressure accumulator is supplied exclusively by low pressure pumps and the high pressure accumulator solely by high pressure pumps. Also in the conventional arrangement the demand for low pressure water is such. as to withdraw a greater amount from the accumulator than can be replenished by a bank of three low pressure pumps as disclosed herein. It is assumed, therefore, that the low pressure bank is incapable of maintaining the desired pressure in the low pressure accumulator. In order to meet the low pressure requirements economically without the addition of more low pressure pumps, the system in ac cordance with the invention functions automatically to switch over the high pressure pumps to the low pressure accumulator when the high pressure requirements are met and there is at the same time a demand registered for low pressure water.

This switch-over action is accomplished by' a pair of two-way fluid control devices, generally designated by numerals 19 and 20, each of which is adapted selectively to supply fluid to one of two outlets. Device 19 is constituted by two poppet valves 21 and 22, each valve having an inlet a, an outlet b, and a valve stem c, such that when the stem is lifted, Water flows from the inlet to the associated outlet. The valve stems 21c and 22c are alternately actuated by a rocker arm 25, operated by a control mechanism 26 which may be in the form of a solenoid, such that in one angular position of the arm valve 21 is open and valve 22 is closed and in the other position valve 21 is closed and valve 22 is open.

Similarly, the two-way fluid control device v2t) is constituted by poppet valves 23 and 24, each having an inlet a, an outlet b and a valve stem 0, the stems being actuated alternately by a rocker arm 27 operated by a control mechanism 28. Control mechanism 26 is operatively coupled to water-level sensing elements C and D, disposed on the high pressure accumulator 12. The sensing elements are mounted at difiierent levels in the accumulator, such that when the water is at the lower or minimum level of element D, indicating depletion of the supply, control mechanism 26 operates to close valve 21 and to open valve 22, whereas when the water is at the higher or maximum level indicated by element 0, control mechanism efiects the reverse valve action. The sensing elements may be in the form of float-operated switches or other known means responsive to water level.

Control mechanism 28 is operatively coupled to sensing In practice, the high pressure pumps may lowerlevel of element A, indicating depletion, valve iscaused to close and valve 26 is opened, whereas when the accumulator is adequately filled, as indicated by element B at the higher level, the control mechanism eifects the reverse valve action.

The bank 11 of low pressure pumps is connected by a conduit 29 to the low pressure accumulator 13, a'check valve 30 being interposed between the accumulator and the pumps to prevent the reverse flow of water. The bank 10 of high pressure pumps is connected 'by a conduit 31 to the inlets a of both valves 21 and 22. The outlet b of valve 22 is connected via 'pipe 32 and a check valve 33 to the high pressure accumulator '12. The outlet b of valve 21 is connected by a'conduit 34 to'the inlets a of both valves 23 and 24, theoutlet'b of valve 24being connected by a-conduit 35 to lowpressure accumulator 13.

The outlet -'b of valve 23 is connected by conduit 36 to a suction tank 37. The lowpressure'pumps of bank 11 are connected through a conduit '38 and a bypass valve 39 to suction-tank 3-7, the operation of theby-pass valve being controlled bya-mechanism 40 responsive to sensing element B such that when the low pressure 'accumulator is filled, valve 39 opens'to discharge water from the low pressure pumps into the JSllClllOIl 'tank'31,

the valve otherwise being closed.

We shall now consider the operation of the system under the various conditions which subsist in the course of operation, namely, (a) when 'both accumulators are filled, (b) when only the low pressure accumulator calls for water, (0-) when only "the. 'high pressure accumulator calls for water, and-(d) "when both accumulators call for water. Itwill' be evident from the following that the system isself-adjusting and'acts'automatically tomaintain the desired level of water 'in both accumulators under. varying load conditions.

Operation. with both accumulators filled We shall assume that both the .high and low pressure pumps are running and that the high and low pressure accumulators are filled. This condition causes sensing element C to open valve .21 and sensing elementB to open valve 23, valves 22 and 24 both being. closed.

The fact that valve 21 is open permits water from the high pressure pumping bank to fiow to valves 23 and .24

and since only valve 23 is open, the water is dumped into.

suction tank 37. The fact that valve .22,is closed Cll'tS ofi high pressure water from bank 10 to the high pressure accumulator 12 and the closureof valve24 .cuts off this Water from the low pressure accumulator 13. Bypass valve 39 is open since sensing elementB indicates a 'full tank. The low pressure water from bank 11 is therefore, dumped into the SllCtiOl'lztZlIlkS 37. Thus when both accumulators are filled, .thesystem operates to dump the water from both pump banks into the suction tank and no water is supplied tothe accumulators.

'The valve operation when both accumulators are filled may be summarized as follows:

-. Condition Effect permits H.-P. water to flow to valves 23, 24. cuts oil flow to H.-P. accumulator.

dumps HAP. water to suction tank.

dumps L.-P. water to suction tank.

Operation when low pressure accumulator calls for water 39 is closed. for the water in low pressure accumulator is below the filled level sensed by element B.

Thus the open valve 21 permits water from the high pressure to flow to valves 23 and 24, and since valve 23 is closed fiow to the suction tank is cut off, the high pressure water feeding through open valve 24 to the low pressure tank. And since valve 22 is closed, the high pressure water flow to the high pressure accumulator is blocked. The closure of by-pass valve 39 causes the low pressure water from the low pressure bank 11 to flow to the low pressure accumulator 13.

It will be evident, therefore, that when there is a call for water from the low pressure accumulator, this demand is met not only by the low pressure pumps but also by the high pressure pumps, assuming that there is no concurrent demand for high pressure water. Hence the high pressure pumps act to supplement the action of the low pressure pumps and substantially reduce the low pressure pump requirement of the system.

The various valve operations, when there is a demand only for low pressure water, may be summarized as follows:

Condition Efiect Valve permits H.-P. water to flow to valves 23, 24. cuts off flow to H.-P. accumulator.

cuts ofi flow to suction tank.

puts H.-P. pumps into L.-P. accumulator. cuts ofi flow to suction tank.

High pressure accumulator calls for water In this condition, sensing element D causes valve 21 to close, cutting off high pressure water to valves 23 and 24. Valve 22 is, however, open, permitting the high pressure water to flow into the high pressure accumulator. The condition of valves 23 and 24 in this situation is immaterial since no water is fed thereto. The low pressure accumulator being filled, valve 39 is open to dump water from the low pressure pumps into the suction tank. Thus the high pressure pumps, when the high pressure accumulator calls for water and the low pressure accumulator is full, operate only to feed the high pressure accumulator. This condition may be summarized as follows:

Valve Condition Effect 21 closed".-. cuts ofl flow to valves 23 and 24. '22 open water from H.-P. pumps goes to H.-P.

accumulator. no agslon.

o. dumps L.-P. pumps tosuctlon.

Both accumulators call for water In this'instance, valves 21 and 23 are closed, valves 22 and 24 are open and valve 39 is closed. Consequently, water from the high pressure pumps goes through valve 22 to the high pressure accumulator but cannot flow through valve 24 to the low pressure accumulator. The low pressure water from pump 11 is fed to the low pressure accumulator. Thus the low pressure pumps feed only the low pressure accumulator and the high pressure pumps feed only the high pressure accumulator.

This condition may be summarized as follows:

5 pressure and low pressure water conditions, such that when both accumulators call for water, the related pumps act to supply same and when only the high pressure accumulator calls for water, the high pressure pumps provide the desired supply, but when only the low pressure accumulator calls for water, then both the high and low pressure pumps respond to the demand, thereby effecting an economy in the low pressure pump requirements.

While there has been shown what is considered to be a preferred embodiment of the invention, it will be manifest that many changes and modifications may be made therein without departing from the essential spirit of the invention. It is intended, therefore, in the annexed claims to cover all such changes and modifications as fall within the true scope of the invention.

What is claimed is:

1. A dual-pressure hydraulic system comprising a high pressure pumping source, a low pressure pumping source, a high pressure accumulator, a low pressure accumula tor, means coupling said low pressure source to said low pressure accumulator to supply fluid thereto, means coupling said high pressure source to said high pressure accumulator to supply fluid thereto, means responsive to a condition in which said high pressure accumulator is at a predetermined maximum fluid level and said low pressure accumulator is at a predetermined minimum fluid level to supply fluid from said high pressure source to said low pressure accumulator, and means responsive to a condition in which said high pressure accumulator is at a predetermined minimum fluid level to disconnect said high pressure source from said low pressure accumulator and to connect same to said high pressure accumulator to supply fluid thereto.

2. A dual-pressure, self-regulating hydraulic fluid pressure system comprising a bank of high pressure pumps and a bank of low pressure pumps, low and high pressure accumulators, said low pressure banks being coupled to said low pressure accumulator to supply fluid thereto, first and second two-way fluid control devices each comprising first and second valves having a common inlet and separate outlets and a control mechanism alternately to open only one of said valves, the high pressure bank being coupled to the inlet of said first device, the first outlet of said first device being connected to the inlet of said second device, the second outlet of said first device being connected to the high pressure accumulator to supply fluid thereto, the first outlet of said second device being connected to a suction tank and the second outlet being connected to said low pressure accumulator, means responsive to fluid level in said high pressure accumulator and operatively coupled to the control mechanism of the first device to open the first valve thereof when the fluid is at a given high level and to open the second valve thereof when said fluid is at a given low level, and means responsive to fluid level in said low pressure accumulator and operatively coupled to said control mechanism of said second device to open the first valve thereof when said fluid is at a given high level and to open the second valve when said fluid is at a given low level.

3. A dual-pressure, self-regulating hydraulic fluid pressure system comprising a bank of high pressure pumps and a bank of low pressure pumps, low and high pressure accumulators, said low pressure banks being coupled to said low pressure accumulator to supply fluid thereto, first and second two-way fluid control devices each comprising first and second valves having a common inlet and separate outlets and a control mechanism alternately to open only one of said valves, the high pressure bank being coupled to the inlet of said first device, the first outlet of said first device being connected to the inlet of said second device, the second outlet of said first device being connected to the high pressure accumulator to supply fluid thereto, the first outlet of said second device being connected to a suction tank and the second being connected to said low pressure accumulator, sensing elements disposed in said high pressure accumulator and operatively coupled to the control mechanism of the first device to open said first valve thereof when the fluid is at a given high level and to open said second valve thereof when said fluid is at a given low level, and sensing elements disposed in said low pressure accumulator and operatively coupled to said control mechanism of said second device to open said first valve thereof when said fluid is at a given high level and to open said second valve when said fluid is at a given low level.

4. A dual-pressure, self-regulating hydraulic fluid pressure system comprising a bank of high pressure pumps and a bank of low pressure pumps, low and high pressure accumulators, said low pressure banks being coupled to said low pressure accumulator to supply fluid thereto, first and second two-way fluid control devices each comprising first and second valves having a common inlet and separate outlets and a control mechanism alternately to open only one of said valves, the high pressure bank being coupled to the inlet of said first device, the first outlet of said first device being connected to the inlet of said second device, the second outlet of said first device being connected to the high pressure accumulator to supply fluid thereto, the first outlet of said second device being connected to a suction tank and the second being connected to said low pressure accumulator, sensing elements disposed on said high pressure accumulator and operatively coupled to the control mechanism of the first device to open said first valve thereof when the fluid is at a given high level and to open said second valve thereof when said fluid is at a given low level, sensing elements disposed on said low pressure accumulator and operatively coupled to said control mechanism of said second device to open said first valve thereof when said fluid is at a given high level and to open said second valve when said fluid is at a given low level, a by-pass valve coupling said low pressure bank to said suction tank and including a control mechanism therefor, and means coupling said bypass control mechanism to the sensing elements of said low pressure accumulator to open said by-pass valve when said accumulator is at said maximum level, thereby to dump said low pressure water in said suction tank.

5. A dual-pressure hydraulic system comprising a bank of high pressure pumps, a bank of low pressure pumps, low and high pressure accumulators, conduit means coupling said low pressure bank to said low pressure accumulator, first and second two-way fluid control devices each having an inlet and first and second outlets and a control mechanism alternately to connect said inlet to one of said outlets, means operatively coupled to the control mechanism of the first device and responsive to the fluid level in said high pressure accumulator to open said first outlet when fluid in said high pressure accumulator is at a predetermined maximum level and to open said second outlet when said fluid is at a predetermined minimum level, said first outlet of said first device being connected to the inlet of said second device, said second outlet of said first device being connected to the high pressure accumulator to supply fluid thereto, means operatively coupled to the control mechanism of said second device and responsive to the fluid level in said low pressure accumulator to open said first outlet when fluid in said low pressure accumulator is at a predetermined maximum level and to open said outlet when said fluid is at a predetermined minimum level, said first outlet of said second device being coupled to a suction tank, said second outlet of said second device being coupled to said low pressure accumulator, a by-pass valve coupling said low pressure bank to said suction tank, and means responsive when said low pressure accumulator is at said maximum level to open said by-pass valve.

6. A dual-pressure hydraulic system comprising a bank of high pressure pumps, a bank of low pressure pumps, low and high pressure accumulators, conduit means-,couplingh-sa-id, 10w pressure banks? tosaid =low pressure accumulator firsti and second two-way fluid control devieeseach having; first andsecond valveshaving a :commoninlet and separate outlets and a control mechanism alternately lLOCOHIJGCt said inlet to one vof said cutlets, fluidzlevel sensing means operatively coupled to the control ,mechanismof the first device zandresponsive to the fluid level in saidhigh pressure accumulator .to openisaid first outlet when fluid insaid high, pressure accumulator isatapredetermined maximumlevel and/to opengsaid second outlet whensaid fluid isvat a predetermined minimum level, said first valve outlet of saidfirstdevice be ing connected to the inlet of saidvsecond.device,isaid\sec- 0nd valve .outletof said first device beingconnected to the high pressure accumulator to supply 'fluid thereto, fluiddevel sensing vmeans loperatively l coupled to the control mechanism of said second device and responsive ,to thefluifd level vin ,sai d- 1 ow pressureaccumulator to open aidjfirst, valve outlet when. fluid, in said low pressure accumulator is atia predetermined maximum level andlto open said valve outlet when said ,fluidwis ata predeterminedminimurnzlevel, saidifirstxvalveoutlet of \saidsec ,pressure accumulator, and .meansures ponsive when-said low pressure accumulatoriisat saidmaximum .level to open said bypass valve.

References ;Cited in the ifilei of. this patent UNITED STATES PATENTS vPrhilipwa.....,.-,--..- Mar. 5, 3190.7 Grigoleit I-...... June :22, 1926 

